Polarization Based Dual-Mode Optical Transceiver

This invention relates to optical sensors, and in particular, it relates to optical sensors that that employ either a polarization-dependent or a polarization-independent transceiver.

The field of optical transceivers has seen significant advancements, particularly in dual-mode operation for managing orthogonal polarizations, such as transverse electric (TE) and transverse magnetic (TM) modes. However, conventional optical transceivers often suffer from crosstalk between transmitted and received signals, leading to degraded system performance. Furthermore, achieving efficient polarization management while ensuring scalability to arrays for advanced applications, such as point cloud generation, remains a challenge.

1 U.S. Pat. Appl. Pub. No. 2024/0195077 describes an integrated photonic platform for a transceiver aperture (see Abstract). The transceiver aperture includes an array of pixels, each of the pixels comprising a photonic radiator comprising one or more ports; a photonic mixer comprising an Rx input and a local oscillator (LO) input; and an optical mixer comprising a Tx input; an input/output port; a first output; and a second output, wherein the input/output port is coupled to the one or more ports of the photonic radiator and the first output is coupled to the Rx input (see Claim).

There exists a need for improved polarization-dependent and polarization-independent optical transceivers capable of minimizing crosstalk, managing polarization efficiently, and being combined into scalable arrays. These advancements are critical for applications such as optical communication systems, sensing, and imaging where precise signal transmission and reception are essential.

The present invention is directed to dual-mode optical transceivers and related methods that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

Embodiments of the present invention provide dual-mode optical transceivers capable of operating with orthogonal polarizations (TE and TM modes) to achieve transmission and reception with minimal crosstalk. The embodiments include both polarization-dependent and polarization-independent transceivers, incorporating photonic mixers and polarization beam splitters for efficient signal management. Embodiments of the present invention further enable scalable arrays of such transceivers using optical power splitters, such as optical switch trees, for applications like point cloud generation, ensuring efficient, accurate, and high-performance optical systems.

Additional features and advantages of the invention will be set forth in the descriptions that follow and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings.

To achieve the above objects, the present invention provides an optical sensor, which includes: an optical transceiver, including a radiation area and an input port and an output port coupled to the radiation area, wherein the radiation area is configured to radiate into space a light signal of a first polarization mode and to receive from the space a light signal containing both the first polarization mode and a second polarization mode, the first and second polarization modes being two perpendicular linear polarization modes including a transverse electric (TE) mode and a transverse magnetic (TM) mode; an optical lens configured to direct the radiated light signal from the optical transceiver toward a target and to direct a back-reflected light from the target to the optical transceiver, wherein the optical sensor is free of any polarization altering optical component between the optical transceiver and the optical lens; and a photonic mixer configured to mix the received light signal with a reference local oscillator signal.

In some embodiments, the optical sensor further includes: a laser configured to generate a coherent light signal; and a power beam splitter configured to direct a portion of the light signal from the laser to the photonic mixer as the local oscillator signal, and to direct another portion of the light signal from the laser to the input port of the optical transceiver; wherein the input port and the output port of the optical transceiver are two separate ports which are mode matched to respectively pass only the first polarization mode and the second polarization mode, and wherein the optical transceiver is configured to pass the second polarization mode of the received light signal via the output port to the photonic mixer.

In some embodiments, the optical sensor further includes: a laser configured to generate a coherent light signal; a power beam splitter configured to direct a portion of the light signal from the laser to the photonic mixer as the local oscillator signal; and a polarization beam splitter and rotator having a first port, a second port, and a third port respectively coupled to the power beam splitter, the photonic mixer, and the optical transceiver, wherein the power beam splitter is further configured to direct another portion of the light signal from the laser to the first port of the polarization beam splitter and rotator, wherein the polarization beam splitter and rotator is configured to pass only the first polarization mode of the other portion of the light signal from the first port to the third port, wherein the input port and the output port of the optical transceiver are a common port coupled to the third port of the polarization beam splitter and rotator and configured passes both the first and the second polarization modes, wherein the optical transceiver is configured to radiate the first polarization mode of the other portion of the light signal from the polarization beam splitter and rotator, and to pass both the first polarization mode and the second polarization mode of the received light signal via the common port to the third port of the polarization beam splitter and rotator, and wherein the polarization beam splitter and rotator is further configured to convert the second polarization mode of the received light signal from the optical transceiver to the first polarization mode and direct the converted light signal to its second port for coupling to the photonic mixer.

In another aspect, the present invention provides an array of optical sensors, which includes: a plurality of the optical sensors described above; a laser configured to generate a coherent light signal; and an optical power splitter and switch tree structure configured to split the coherent light signal of the laser among the plurality of the optical sensors.

In some embodiments, the optical power splitter and switch tree structure includes one or more components selected from a group consisting of: Mach-Zehnder modulators, thermal modulators, and PIN modulators.

In some embodiments, the optical power splitter and switch tree structure is configured to supply light signals to the plurality of the optical sensors simultaneously.

In some embodiments, the optical power splitter and switch tree structure is configured to supply light signals to the plurality of the optical sensors at different times.

In some embodiments, each of the plurality of optical sensors further includes a power beam splitter configured to direct a portion of the light signal from the optical power splitter and switch tree structure to the photonic mixer as the local oscillator signal, and to direct another portion of the light signal from the optical power splitter and switch tree structure to the input port of the optical transceiver; wherein the input port and the output port of the optical transceiver are two separate ports which are mode matched to respectively pass only the first polarization mode and the second polarization mode, and wherein the optical transceiver is configured to pass the second polarization mode of the received light signal via the output port to the photonic mixer.

In some embodiments, each of the plurality of optical sensors further includes: a power beam splitter configured to direct a portion of the light signal from the optical power splitter and switch tree structure to the photonic mixer as the local oscillator signal, a polarization beam splitter and rotator having a first port, a second port, and a third port respectively coupled to the power beam splitter, the photonic mixer, and the optical transceiver, wherein the power beam splitter is further configured to direct another portion of the light signal from the optical power splitter and switch tree structure to the first port of the polarization beam splitter and rotator, wherein the polarization beam splitter and rotator is configured to pass only the first polarization mode of the other portion of the light signal from the first port to the third port, wherein the input port and the output port of the optical transceiver are a common port coupled to the third port of the polarization beam splitter and rotator and configured passes both the first and the second polarization modes, wherein the optical transceiver is configured to radiate the first polarization mode of the other portion of the light signal from the polarization beam splitter and rotator, and to pass both the first polarization mode and the second polarization mode of the received light signal via the common port to the third port of the polarization beam splitter and rotator, and wherein the polarization beam splitter and rotator is further configured to convert the second polarization mode of the received light signal from the optical transceiver to the first polarization mode and direct the converted light signal to its second port for coupling to the photonic mixer.

In another aspect, the present invention provides a method for transmitting an optical signal and detecting a back-reflected optical signal using an optical sensor, which includes: generating a coherent light signal; splitting the light signal using a power beam splitter and directing a portion of the light signal to a photonic mixer as a local oscillator signal, and directing another portion of the light signal to an input port of an optical transceiver; passing only a first polarization mode of the other portion of the light signal through the input port of the optical transceiver to a radiation area of the optical transceiver, and radiating the first polarization mode into space as a radiated light signal; directing the radiated light signal from the optical transceiver toward a target and directing a back-reflected light from the target to the optical transceiver, without altering polarization modes of the radiated light signal and the back-reflected light signal, wherein the back-reflected light signal contains both the first polarization mode and a second polarization mode, wherein the first and second polarization modes are two perpendicular linear polarization modes including a transverse electric (TE) mode and a transverse magnetic (TM) mode; capturing the back-reflected light signal by the radiation area of the optical transceiver, including both the first polarization mode and a second polarization mode; coupling only the second polarization mode of the captured light signal to an output port of the optical transceiver; directing the light signal from the output port of the optical transceiver into the photonic mixer; and coherently mixing the local oscillator signal and the received signals from the optical transceiver in the photonic mixer to generate In-phase and Quadrature-phase (IQ) signals.

In another aspect, the present invention provides a method for transmitting optical signals and detecting a back-reflected optical signals using a plurality of optical sensors, which includes: performing the method described above by each of the plurality of optical sensors, wherein the step of generating the coherent light signal includes: generating a coherent input light using a laser; and splitting the coherent input light of the laser among the plurality of the optical sensors using an optical power splitter and switch tree structure, to supply the coherent light signals, wherein coherent light signals are either supplied to the plurality of the optical sensors simultaneously, or supplied to the plurality of the optical sensors at different times.

In another aspect, the present invention provides a method for transmitting an optical signal and detecting a back-reflected optical signal using an optical sensor, which includes: generating a coherent light signal; splitting the light signal using a power beam splitter and directing a portion of the light signal to a photonic mixer as a local oscillator signal, and directing another portion of the light signal to a first port of a polarization beam splitter and rotator; the polarization beam splitter and rotator passing only the first polarization mode of the other portion of the light signal from the first port to a third port of the polarization beam splitter and rotator; an optical transceiver receiving the first polarization mode of the other portion of the light signal from the third port of the polarization beam splitter and rotator, and radiating the first polarization mode into space as a radiated light signal; directing the radiated light signal from the optical transceiver toward a target and directing a back-reflected light from the target to the optical transceiver, without altering polarization modes of the radiated light signal and the back-reflected light signal, wherein the back-reflected light signal contains both the first polarization mode and a second polarization mode, wherein the first and second polarization modes are two linear perpendicular polarization modes including a transverse electric (TE) mode and a transverse magnetic (TM) mode; capturing the back-reflected light signal by the radiation area of the optical transceiver, including both the first polarization mode and a second polarization mode; directing the captured light including both the first and the second polarization modes form the optical transceiver to the third port of the polarization beam splitter and rotator; the polarization beam splitter and rotator converting the second polarization mode of the received light signal on its third port to the first polarization mode and directing the converted light signal via its second port to the photonic mixer; and coherently mixing the local oscillator signal and the received signals from the optical transceiver in the photonic mixer to generate In-phase and Quadrature-phase (IQ) signals.

In another aspect, the present invention provides a method for transmitting optical signals and detecting a back-reflected optical signals using a plurality of optical sensors, which includes: performing the method described above by each of the plurality of optical sensors, wherein the step of generating the coherent light signal includes: generating a coherent input light using a laser; and splitting the coherent input light of the laser among the plurality of the optical sensors using an optical power splitter and switch tree structure, to supply the coherent light signals, wherein coherent light signals are either supplied to the plurality of the optical sensors simultaneously, or supplied to the plurality of the optical sensors at different times.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

1 FIG. 1 FIG. 101 103 104 102 104 102 100 101 102 Generally, as illustrated in, when a linearly polarized lightshines on a target, the back-reflected light() from the target experiences a light scattering that affects its amplitude and polarization. In terms of the amplitude, a part of the power is absorbed by the target due to material loss, a part of it passes through the target, and the rest is backscattered. The scattered lighthas, in general, a Lambertian profile. The polarization status of the back-reflected lightis changed such that it experiences a polarization conversion, and other possible polarizations (different from that of the incident light) can be generated. Therefore, for an optical sensor (an optical lensof the optical sensor is schematically shown in), if the transmitted light (Tx)(i.e. the incident light on the target) is a TE polarized light, the back-reflected light (Rx)from the target will have both TE and TM polarizations.

2 FIG. 200 201 202 208 204 203 schematically illustrates a coherent optical sensor that employs a polarization-dependent optical transceiver according to a first embodiment of the present invention. The input light from a laser sourceis a coherent light that contains only the TE mode (if the light originally contains both polarization modes, the TM mode will be filtered out). The input light is split by a power beam splitterinto two parts. A smaller part, LO signal, is for a local oscillator (LO) and is directed to a photonic mixerto be mixed with the received signal. A larger partis directed into a transmitting path Txfor radiation to the space through the transceiver.

205 205 203 204 207 205 205 204 The optical transceiveris a polarization-dependent element having two ports which are respectively polarization matched to the two linear polarization modes, i.e., they only pass the matched polarization modes. One port (input port or Tx port) of the transceiveris coupled to the transmitting path Txto pass the optical signalto be transmitted, and the other port (output port or Rx port) is coupled to a receiving path Rxfor transmitting back-reflected optical signals received by the transceiver. Both ports work with a fundamental waveguide mode, i.e., TE polarization. It should be noted that due to the construction of the transceiver(e.g., a 2D grating described in more detail later), a linear polarization that is TE mode from the standpoint of one port is TM mode from the standpoint of the other port and vice versa. The radiation area of the transceiverradiates the signalfrom the Tx port to the space.

2 FIG. 100 101 102 205 205 205 100 205 102 205 205 203 201 200 205 205 206 207 208 203 207 also schematically illustrates the optical lensof the coherent optical sensor, the transmitted light signal Tx, and the back-reflected light signal Rxfrom the target. The radiation area of the transceiverreceives (captures) the back-reflected light signal. The transmitter and receiver are the same device (the transceiver), thus the transmitted signal and the received signal travel the same optical path between the target and the transceiver. No quarter wave plate or other polarization altering optical component is used in the optical sensor to change the polarization state of the transmitted and received light between the transceiverand the target. The light transmitted from the lensto the target is the linearly polarized light (e.g. TE from the standpoint of the Tx port) emitted by the transceiver. Due to scattering effects and polarization conversion by the target, the back-reflected light signal Rxcontains both linearly polarized components, i.e., both the same polarization as the transmitted signal (referred to as the unrotated polarization mode) and the orthogonal polarization (referred to as the rotated polarization mode). The unrotated mode of the back-reflected light received by the radiation area of the transceiver, which is TE mode from the standpoint of the Tx port, is back-coupled by the polarization-dependent transceiverinto the Tx path, which will pass through the beam splitterand be absorbed by an optical isolator inside the laser. The rotated mode of the light received by the transceiver, which is TM mode from the standpoint of the Tx port but is TE mode from the standpoint of the Rx port, is polarization matched with the Rx port, so it is coupled by the transceiverto that port (as signal) and directed along Rx pathto the photonic mixer. The optical pathsandmay be optical waveguides or free space optical paths, or combinations thereof.

205 The polarization-dependent transceiverensures that there is no crosstalk between the transmitted and received signals.

202 206 207 208 208 The LO signaland the back-reflected signalfrom the Rx pathare mixed coherently in the photonic mixerto generate a mixed signal for detection. The photonic mixermay include a 90-degree hybrid and two balanced photodetectors (BPD), which are for generating In-phase (I) and Quadrature-phase (Q) signals. Photonic mixers are generally known in the art and can be implemented by any suitable structures.

4 4 a b FIGS.and 4 a FIG. 3 FIG. 4 b FIG. 3 FIG. 4 FIG. 406 404 406 402 Compared to the structure shown inof US 2024/0195077 (“the ‘077 publication”), which uses a dual channel transceiver(see), it can be seen that the structure in the ‘077 publication requires a quarter wave plate QWPbetween the transceiverand the lensto change the polarization of the outgoing and returning beams, whereas in the embodiment shown inof the present invention, no quarter wave plate or other polarization altering optical component is required. The structure in the ‘077 publication relies on the target's ability to convert between two circular polarized lights (e.g. LHCP (left-hand circular polarized) to RHCP (left-hand circular polarized) light) due to the reflection and polarization rotation (see). The embodiment of the present invention shown in, however, relies on the target's ability to scatter the light and generate both linearly polarized lights (TM and TE). The device ofof the ‘077 publication does not contemplate utilizing the target's ability to scatter the light and generate both linearly polarized lights for the detection system.

3 FIG. 2 FIG. 2 FIG. 201 200 202 204 203 300 300 203 207 302 302 300 schematically illustrates a coherent optical sensor that employs a polarization-independent optical transceiver according to another embodiment of the present invention. Similar to the embodiment of, a power beam splittersplits the coherent input light (TE mode) form the laser sourceinto a LO signaland a Tx signalfor the transmitting path Tx. Different from the embodiment of, here, a polarization beam splitter and rotator (PBSR)with at least three ports (e.g., two input ports and one output port) is provided, which can convert (rotate) between TE and TM polarizations and direct them along separate optical paths. One port (e.g., a first input port) of the PBSRis coupled to the transmitting path Tx, another port (e.g., the second input port) is coupled to the receiving path, and the third port (e.g., the output port) is coupled to the optical transceiver. In this embodiment, the transceiveris a polarization-independent element with one port which is coupled to the output port of the PBSR, where the port can pass both polarization mode signals.

204 203 300 302 302 102 301 302 302 300 301 301 301 300 204 301 303 300 207 202 303 300 208 The Tx signal(TE mode) on the Tx pathpasses through the PBSRfrom its first input port to its output port to enter the transceiver, which then radiates the signal to the space. Again, no quarter wave plate or other polarization altering optical component is used in the optical sensor to change the polarization state of the transmitted and received light between the transceiverand the target. Due to scattering effects and polarization conversion by the target, the back-reflected light Rxcontains both TE and TM mode components. The received signal Rxoutput by the polarization-independent transceivercorrespondingly contains both TE and TM mode components. In this embodiment, the input port and the output port of the transceiverare the same port, which can pass both TE and TM polarization modes in both directions. This port is coupled to the output port of the PBSRto transmit the receive signal Rxto the PBSR. The received signal Rxis split by the PBSR into two parts. The TE mode of the received signal Rxpasses through the PBSRfrom its output port to its first input port and travels back in the Tx path. The TM mode of the received signal Rxis converted into TE modeby the PBSRand directed via its second input port into the receiving path Rx. The LO signaland the Rx signalsfrom the PBSR(both TE) are mixed coherently in the photonic mixerto generate a mixed signal for detection.

The PBSR in this embodiment facilitates efficient polarization management to ensure minimal signal loss and no crosstalk between the TE and TM modes.

2 b FIG. 2 2 a b FIGS.and 2 FIG. 2 FIG. 4 FIG. 204 210 302 Compared to the structure shown inof the ‘077 publication, which uses a single channel photonic transceiver (photonic radiator), the structure in the ‘077 publication does not use a PBS or a QWP for operations (see the ‘077 publication, paragraph [0022]; note that the optical mixershown inis not a PBSR), whereas in the embodiment shown inof the present invention, a PBSR is used in conjunction with a single channel transceiver. Neither embodiment (and) of the ‘077 publication contemplates utilizing the target's ability to convert between two linearly polarized lights for the detection system.

205 302 400 401 402 404 403 402 404 4 4 4 FIGS.A,B andC 4 FIG.A 4 FIG.B 4 FIG.C In the above embodiments, the polarization-dependent transceiverand the polarization-independent transceivermay be implemented by various structures, as schematically illustrated in.illustrates a 2D grating couplerwhich may be used as a polarization-dependent transceiver. One polarization light (e.g., TE) from one port can be radiated through the grating in a normal direction. The 90-degree rotated polarization light can be coupled into the other port because it is polarization matched with that port.illustrates a 1D grating couplerwhich may be used as a polarization-independent transceiver. This grating can be designed to have a similar and large coupling efficiency for both TE and TM polarizations.illustrates an edge coupler waveguide made from Si or SiN which may be used as a polarization-independent transceiver. The structure includes a Si substrate, a waveguiding layerwhich may be either Si or Si3N4 or any other suitable material that guides optical light, and a SiO2 spacing layerlocated between the substrateand the waveguiding layer. The edge coupler can be designed so that the coupling efficiency for both TE and TM polarizations can be similar and large. These transceivers are known devices and can be implemented by those of ordinary skill in the relevant art. Other suitable devices may also be used to implement the transceivers.

5 FIG. 2 FIG. 205 208 201 202 208 204 203 205 200 500 500 schematically illustrates a coherent optical sensor array formed of multiple distinct single element sensors each employing a polarization-dependent transceiver according to another embodiment of the present invention. Each sensor is similar to that shown in the embodiment in, and includes a polarization-dependent transceiver, a photonic mixer, and a power beam splitterthat splits the input light into a LO signaldirected to the photonic mixerand a Tx signaldirected to the transmitting path Txof the transceiver. The light from the laser sourceis split by an optical power splitter and switch tree structureinto multiple paths that respectively provide input light to the multiple sensors. The optical power splitter and switch treecan either split the power (e.g., equally) among the multiple optical sensors and supply them simultaneously, or direct the light into different optical sensors at different times, including supplying a subset of the multiple optical sensors simultaneously and supplying different subsets at different times. The optical power splitter and switch tree can be implemented by thermal modulators, PIN modulators, Mach-Zehnder modulator, a combination of the above, etc. Optical switch trees are generally known in the relevant art.

205 5 FIG. The multiple polarization-dependent transceiversmay be arranged to form an array of multiple transceiver pixels. A common lens (not shown in) is provided for the sensor array. The array can help to increase the field of view (FOV) of the sensor array compared to a single element device. The sensor array can also be used to steer the emitted light in space. When each of the elements is turned on, the light from that transceiver hits a different area on the lens of the sensor array, which causes that light to be bent and transmitted to a specific direction in space. Therefore, each transceiver sends light to a different direction in space.

6 FIG. 3 FIG. 6 FIG. 5 FIG. 302 300 302 203 207 208 201 202 208 203 schematically illustrates a coherent optical sensor array formed of multiple distinct single element sensors each employing a polarization-independent transceiver according to another embodiment of the present invention. Each sensor is similar to that shown in the embodiment in, and includes a polarization-independent transceiver, a PBSRcoupled to the transceiveras well as to the transmitting path Txand the receiving path Rx, a photonic mixer, and a power beam splitterthat splits the input light into a LO signaldirected to the photonic mixerand a Tx signal directed to the transmitting path Tx. Other aspects of the embodiment ofare similar to those of the embodiment of.

5 6 FIGS.and The optical sensor arrays described above and shown inmay be used to form a system for generating a point cloud. The optical sensor array generates a point cloud by leveraging the dual-mode operation of the transceivers to capture signals in both TE and TM polarizations.

It will be apparent to those skilled in the art that various modification and variations can be made in the optical transceivers, optical sensors and sensor arrays of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents.